Apparatus and method for X2 interface setup and cell switching in mobile communication system

ABSTRACT

A method and an apparatus for setting up an X2 interface setup are provided. The method includes transmitting, by a first Base Station (BS), an X2 interface setup request to a second BS, wherein the X2 interface setup request comprises an access mode of a Closed Subscriber Group (CSG) supported by a cell in the first BS, and transmitting, by the second BS, an X2 interface response message to the first BS, wherein the X2 interface response message comprises the access mode of the CSG supported by the cell in the second BS.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of a Chinesepatent application filed in the Chinese Intellectual Property Office onApr. 28, 2010 and assigned Serial No. 201010159944.5, the entiredisclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to mobile communication technologies. Moreparticularly, the present invention relates to an X2 interface setupmethod and a cell switching method in a mobile communication system.

2. Description of the Related Art

Along with recent developments of mobile communication technologies, aSystem Architecture Evolution (SAE) system has been widely used. Morespecifically, the SAE system includes an Evolved Universal TerrestrialRadio Access Network (E-UTRAN) and a core network.

FIG. 1 is a diagram illustrating an SAE system architecture according tothe related art. A Base Station (BS) under the SAE system belongs to theE-UTRAN 110, and is responsible for providing User Equipment (UE) with aradio interface for accessing the SAE system. A Mobile Management Entity(MME) and a user plane entity (i.e., a Serving GateWay (S-GW)) 150belong to the core network, and are connected with the BS under the SAEsystem through an S1 interface. Here, it is possible that the MME andthe S-GW 150 are located in the same physical entity. FIG. 1 illustratesan example in which the MME and the S-GW 150 are located in the samephysical entity, which is denoted as MME/S-GW. More specifically, theMME is responsible for managing a session context and/or a mobilecontext of the UE and saving security-related-information of a user, andthe S-GW provides a user plane function.

Referring to FIG. 1, the BS under the SAE system includes a home BS 130(e.g., a Home enhanced Node B (HeNB) or Home Node B (HNB)) and anordinary macro BS 120 (e.g., enhanced Node B (eNB)). More specifically,the home BS 130 is used for a family and can be applied to places suchas a university and/or a company, and is a plug-and-play type. That is,the HeNB is the home BS 130 applied to a long term evolution system andis connected with a gateway 140 of the home BS 130 through the S1interface, and the gateway 140 of the home BS 130 is connected with theMME/S-GW 150 through the S1 interface. The HeNB may also be directlyconnected with the MME/S-GW 150 without the gateway of the BS. The HNBis the home BS 130 applied to a Universal Mobile TelecommunicationsSystem (UMTS) system and is connected with the gateway of the BS throughan Iuh interface, and the gateway of the BS is connected with a ServingGPRS Support Node (SGSN) through the Iuh interface. Typically, the homeBS 130 has a limit for an accessed UE, i.e., only the UE having anauthority for accessing the home BS 130 can access the home BS 130,which is different from the ordinary macro BS 120. For example,regarding the user's family, only a member of the user's family oranother member permitted by this family can access the home BS 130 ofthe family. Regarding a company, only a staff of the company and acooperation partner permitted by this company can have access.

Typically, a group of home BSs having the same access user group (e.g.,the home BSs used for the same company) is denoted as a ClosedSubscriber Group (CSG). There is a unique IDentifier (ID) for each CSG,and the CSG ID is broadcasted in broadcast information of the home BS.In the related art, in order for the home BS to provide increasedcoverage, three access modes, which respectively are a Closed mode, aHybrid mode and an Open mode, are defined for a cell of the home BS. Thethree access modes are respectively described in more detail below.

If the access mode of the cell of the home BS is the Closed mode, only aparticular user, i.e., a user having a subscription with an operator,can access the cell of the home BS. A supported CSG ID is broadcasted inthe cell of the home BS. Typically, the cell of this home BS in whichthe CSG ID is broadcasted and the access mode, which is the Closed mode,is denoted as a CSG cell. That is, the CSG cell denotes a closed-modecell which supports a CSG function. If the access mode of the cell ofthe home BS is the Hybrid mode, the cell is denoted as a Hybrid cell. Itis also required to broadcast the supported CSG ID in the Hybrid cell.Any of the users can access this Hybrid cell, but the member thatbelongs to the CSG supported by this Hybrid cell, i.e., the user alreadyhaving a subscription with the operator, can gain a better service. Thatis, in the event that the Hybrid cell has a limited resource, firstlythe member that does not belong to this home BS is switched to anothercell, or is provided with a service using a low Quality of Service(QoS). If the access mode of the home BS is the Open mode, the home BSis the same as a macro cell, i.e., any user is permitted to have access.Also, no CSG ID is allocated to the cell of the home BS, and no CSG IDis broadcasted. The cell of the home BS of the Open mode is no differentfrom the ordinary macro BS, and is denoted as an Open cell hereinafter.

Typically, a list of the CSG ID which permits access of the UE is savedon both the UE and the MME. This list may be subscription information.When the user accesses the cell of the home BS, the UE and the MMEperform access control. That is, if it is determined that the accessmode of the cell of the target home BS to be accessed by the user is theClosed mode, the user is permitted to have access in the event that theCSG supported by the cell of the home BS belongs to the list of the CSGID which permits access. If the access mode of the cell of the home BSis the Hybrid mode, the user is permitted to have access and it isdetermined that the user is the member of the home BS in the event thatthe CSG supported by the cell of the home BS belongs to the list of theCSG ID which permits access, and the user is permitted to have accessand it is determined that the user is not the member of the home BSotherwise.

Typically, a situation in which the UE moves from a home BS to anotherhome BS, and particularly in which the UE moves from among multiple homeBSs which belong to the same CSG, frequently occurs. With respect tothis situation, handover based on the S1 interface (which is alsodenoted as a S1 handover) and handover based on an X2 interface (whichis also denoted as an X2 handover) are the most common measures. Morespecifically, being compared with the X2 handover, the S1 handover hasshortcomings such as frequent signaling interaction and/or core networkrequirements. A specific X2 handover procedure is as follows. When theUE of a connected mode moves from an eNB1 to another eNB2, if there isan X2 interface between the two eNBs, the eNB1 transmits a message tothe eNB2 and the eNB2 prepares a resource. Thereafter, the eNB1 notifiesa new configuration of a target cell to the UE, and the UE issynchronized with the target cell and transmits a message to notify thetarget cell. The BS in which the target cell is located, i.e., the eNB2,transmits a message to the MME after receiving the notification from theUE, so that the MME switches a downlink data tunnel from a source cellto the target cell.

It can be found that the X2 interface handover procedure in the relatedart is completely performed with respect to the macro BS eNB. The mainreason for this is that in a system structure, which is illustrated inFIG. 1, there is an X2 interface between the macro BSs and there is noX2 interface between the home BSs. Therefore, the UE does not movebetween the home BSs.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide an apparatus and method for performing ahandover between home Base Stations (BSs) in a mobile communicationsystem.

Another aspect of the present invention is to provide an apparatus andmethod for performing a handover between home BSs using an X2 interfacein a mobile communication system.

Another aspect of the present invention is to provide an apparatus andmethod for establishing an X2 interface between home BSs in a mobilecommunication system.

In accordance with an aspect of the present invention a method forsetting up an X2 interface in a mobile communication system is provided.The method includes transmitting, by a first Base Station (BS), an X2interface setup request to a second BS, wherein the X2 interface setuprequest comprises an access mode of a Closed Subscriber Group (CSG)supported by a cell in the first BS, and transmitting, by the second BS,an X2 interface response message to the first BS, wherein the X2interface response message comprises the access mode of the CSGsupported by the cell in the second BS.

In accordance with another aspect of the present invention a method forcell switching in a mobile communication system is provided. The methodincludes determining, by a source BS, whether to permit a handover of aUser Equipment (UE) based on access mode of a target BS, transmitting,by the source BS, a handover request to the target BS, wherein thehandover request comprises a group member state indication of the UE,and transmitting, by the target BS, a handover response to the sourceBS.

In accordance with still another aspect of the present invention anapparatus for a BS in a mobile communication system is provided. Theapparatus includes a communication unit for transmitting an X2 interfacesetup request to a second BS, wherein the X2 interface setup requestcomprises an access mode of a CSG supported by a cell in the first BS,and for receiving an X2 interface response message from the second BS,wherein the X2 interface response message comprises the access mode ofthe CSG supported by the cell on the second BS, and a storage unit forstoring the access mode of the CSG supported by the cell in the secondBS.

In accordance with yet another aspect of the present invention anapparatus for a BS in a mobile communication system is provided. Theapparatus includes a controller for determining whether to permit ahandover of an UE based on access mode of a target BS, a communicationunit for transmitting a handover request to the target BS, wherein thehandover request comprises a group member state indication of the UE,and for receiving a handover response from the target BS.

In accordance with a further aspect of the present invention anapparatus for a BS in a mobile communication system is provided. Theapparatus includes a communication unit for receiving a handover requestcomprising a CSG IDentifier (ID) supported by the target cell which isreported from the UE, and a controller for determining whether the CSGID included in the handover request is consistent with the CSG IDsupported by the target cell before transmitting the access request,wherein the communication unit transmits the access request to a MobileManagement Entity (MME) when the CSG IDs are consistent, and transmits ahandover failure message to the source BS when the CSG IDs are notconsistent.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagram illustrating a System Architecture Evolution (SAE)system architecture according to the related art;

FIG. 2 is a diagram illustrating a procedure for setting up an X2interface according to an exemplary embodiment of the present invention;

FIG. 3 is a diagram illustrating an SAE system architecture according toan exemplary embodiment of the present invention;

FIG. 4 is a diagram illustrating a procedure of a User Equipment (UE)accessing a source cell required to handover to a target cell accordingto an exemplary embodiment of the present invention;

FIG. 5 is a diagram illustrating a procedure of a UE accessing a sourcecell required to switch to a target cell according to an exemplaryembodiment of the present invention;

FIG. 6 is a diagram illustrating a procedure of a UE accessing a sourcecell in a source Base Station (BS) required to switch to a target cellin a target BS according to an exemplary embodiment of the presentinvention;

FIG. 7 is a diagram illustrating a procedure of a UE accessing a sourcecell in a source BS required to switch to a target cell in a target BSaccording to an exemplary embodiment of the present invention;

FIG. 8 is a block diagram of a BS in a mobile communication systemaccording to an exemplary embodiment of the present invention; and

FIG. 9 is a block diagram of a Mobile Management Entity (MME) in amobile communication system according to an exemplary embodiment of thepresent invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. Also, descriptions of well-known functions and constructionsare omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention are provided for purposes of illustration only and notfor the purpose of limiting the invention as defined by the appendedclaims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to skill in theart, may occur in amounts that do not preclude the effect thecharacteristic was intended to provide.

Exemplary embodiments of the present invention provide a home BaseStation (BS) entity involved in Closed Subscriber Group (CSG)principles. An example of the home BS includes a Home enhanced Node B(HeNB). It should be understood that technical solutions according tothe exemplary embodiments of the present invention are also applicableto a macro BS in which the CSG is defined. For example, if a cell of themacro BS is also defined with the CSG and can also be divided into a CSGcell, a Hybrid cell and an Open cell according to an access mode, theCSG cell, the Hybrid cell and the Open cell, which are described in moredetail below, can be the cells applied to the macro BS.

FIG. 2 is a diagram illustrating a procedure for setting up an X2interface according to an exemplary embodiment of the present invention.The procedure is applied to a scenario in which the X2 interface isestablished between the home BSs which belongs to the same CSG, and isalso applicable to a scenario in which the X2 interface is establishedbetween the home BS and the macro BS or a scenario in which the X2interface is established between the macro BSs.

Referring to FIG. 2, in step 201, a BS 210 transmits an X2 interfacesetup request to a BS 220. Here, if the BS 210 supports a CSG function,the access mode of the CSG supported by the cell on the BS 210 isincluded in the X2 interface setup request. More specifically, theaccess mode of the CSG can be implemented as at least one of a Closedmode, a Hybrid mode and an Open mode as described in the related art. Ifthe access mode of the CSG is the Closed mode or the Hybrid mode, a CSGIDentifier (ID) supported by the cell on the BS 210 can be furtherincluded in the X2 interface setup request. If the access mode of theCSG is the Open mode, there is no need to include the CSG ID supportedby the cell on the BS 210 in the X2 interface setup request since thereis no CSG ID for the cell of the Open mode, and it is sufficient toinclude only the access mode of the CSG supported by the cell on the BS210, i.e., the Open mode. In an exemplary implementation, the X2interface setup request can further include an identifier of the BS 210,and/or information of the cell on the BS 210. Optionally, the requestcan include at least one of information of an adjacent cell of the BS210, and information of a Mobile Management Entity (MME) pool to whichthe BS 210 belongs.

In step 203, the BS 220 transmits an X2 interface response message tothe BS 210. Here, if the BS 220 supports a CSG function, the access modeof the CSG supported by the cell on the BS 220 is included in the X2interface response message. More specifically, the access mode of theCSG can be implemented as at least one of the Closed mode, the Hybridmode and the Open mode as described above with respect to the relatedart. If the access mode of the CSG is the Closed mode or the Hybridmode, the CSG ID supported by the cell on the BS 220 can be furtherincluded in the X2 interface response message. If the access mode of theCSG is the Open mode, there is no need to include the CSG ID supportedby the cell on the BS 220 in the X2 interface response since there is noCSG ID for the cell of the Open mode, and it is sufficient to includeonly the access mode of the CSG supported by the cell on the BS 220,i.e., the Open mode. In an exemplary implementation, the X2 interfaceresponse message can further include an identifier of the BS 220, and/orinformation of the cell on the BS 220. Optionally, the message caninclude at least one of information of an adjacent cell of the BS 220,and information of an MME pool to which the BS 220 belongs.

The X2 interface setup method provided according to an exemplaryembodiment of the present invention is implemented as described above.According to the setup method, the system structure illustrated in FIG.1 can be updated as illustrated in FIG. 3.

FIG. 3 is a diagram illustrating a System Architecture Evolution (SAE)system according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the SAE system belongs to an Evolved UniversalTerrestrial Radio Access Network (E-UTRAN) 310. In the SAE system, ahome BS 330 is connected with a gateway 340 of the home BS 330 through51 interface, and the gateway 340 of the home BS 330 is connected with aMME/Special GateWay (S-GW) 350 through 51 interface. A macro BS 320 isconnected with the MME/S-GW 350 through 51 interface. More particularly,the X2 interface is set up between macro BSs 320 and X2 interface is setup between home BSs 330.

A cell switching method in the mobile communication system according toan exemplary embodiment of the present invention is described below withreference to FIG. 4.

FIG. 4 is a diagram illustrating a procedure of a User Equipment (UE)accessing a source cell required to handover to a target cell accordingto an exemplary embodiment of the present invention. The exemplaryembodiment of the present invention is applied to the system structureillustrated in FIG. 3. It is assumed herein that a source cell on asource BS and a target cell on a target BS are both cells supporting aCSG function and correspond to the same CSG, i.e., a CSG ID broadcastedin the source cell is the same as that in the target cell. Also, an X2interface has been established in accordance with the method illustratedin FIG. 2 by the source BS and the target BS.

Referring to FIG. 4, in step 401, the UE 410 transmits a measurementreport to the source BS 420 in which the source cell is located. Here,the UE 410 transmits the measurement report according to a configurationof the source cell. For example, if it is specified in the configurationof the source cell that the UE 410 transmits the measurement reportperiodically, the UE 410 transmits the measurement report in a presettime interval. If it is specified in the configuration of the sourcecell that the measurement report is triggered by an event, i.e., istransmitted when a certain condition is met, the UE 410 transmits themeasurement report when the event is satisfied. Here, a physical layeridentifier corresponding to the target cell is included in themeasurement report, i.e., the source BS 420 knows the target cell towhich the UE 410 is to be switched. The source cell and the target cellboth may be cells supporting the CSG function. Thus, the CSG identifierand a group member state indication of the UE 410 can be furtherincluded in the measurement report. More specifically, if the groupmember state indication is set as Member, it is indicated that the UE410 is a user member that belongs to the Hybrid cell.

In step 403, the source BS 420 determines whether it is permitted tohandover the UE 410 to the target cell. If the handover is permitted,the source BS 420 transmits a handover request to the target BS 430 instep 405. Otherwise, the source BS 420 refuses to handover the UE 410 tothe target cell and terminates the procedure. The source BS 420 can makethe determination according to an algorithm for radio resourcemanagement and the measurement report in step 403. More specifically,the source BS 420 determines whether a signal of the target cell meets ahandover condition defined by the algorithm for radio resourcemanagement. If it is determined that the signal of the target cell meetsthe handover condition, the source BS 420 determines whether to handoverthe user to the target cell. The source cell in the source BS 420 andthe target cell in the target BS 430 both may be cells supporting theCSG function and correspond to the same CSG. Also, when the X2 interfacebetween the source BS 420 and the target BS 430 is established by themethod illustrated in FIG. 2, the source BS 420 can obtain informationof the CSG supported by the cell in the target BS 430, e.g., the accessmode of the CSG. Also, in the event that the access mode is the Closedmode or the Hybrid mode, the information of the CSG can further includethe CSG ID supported by the cell in the target BS 430. Thus, whendetermining that the signal of the target cell meets the handovercondition defined by the algorithm for radio resource management, thesource BS 420 can also perform a CSG detection function, i.e., determinewhether the CSG ID supported by the target cell is consistent with thatreported in the measurement report by the UE 410. If it is determinedthat the CSG ID is consistent, the source BS 420 permits the handover ofthe UE 410 to the target cell Otherwise, the source BS 420 refuse tohandover the UE 410 to the target cell if the target cell is the CSGcell.

In step 405, the source BS 420 transmits a handover request to thetarget BS 430. Here, at least one of an indication of an X2 signalingcontext allocated to the UE 410 by the source BS 420, an indication by acore network, an indication of an S1 signaling context allocated to theUE 410 by the core network, an identifier of the target cell, encryptioninformation and an encryption capability of the UE 410, information of aRadio Resource Control (RRC) context and information of an E-UTRAN RadioAccess Bearer (E-RAB) may be included in the handover request. Theinformation of the RRC context includes an access layer configurationand an identifier allocated to the UE 410 by the source cell, and theinformation of the E-RAB includes Quality of Service (QoS) informationand user plane tunnel information of the core network.

When the X2 interface is established by the method illustrated in FIG.2, the source BS 420 obtains the information of the CSG supported by thecell in the target BS 430. Thus, when the source BS 420 transmits ahandover request to the target BS 430 in step 405, if the source BS 420knows that the target cell and the source cell support the same CSGaccording to the obtained information of the CSG supported by the cellin the target BS 430, the target cell should also permit the UE 410 tohave access in the event that the access mode of the source cell is theClosed mode and the UE 410 has already been connected to the source cell(which means that the source cell permits this UE 410 to have access),since the target cell and the source cell support the same CSG.Therefore, if the access mode of the source cell is the Closed mode, thesource BS 420 transmits the handover request to the target BS 430.Thereafter, after receiving the handover request, the target BS 430 canthen determine that the UE 410 is permitted to access the target cell.

In the event that the access mode of the source cell is “Hybrid”, thegroup member state indication of the UE 410 can be further included inthe handover request. More specifically, the group member stateindication can be set as “being a group member” or “not a group member”.Here, since the target cell supports the same CSG as the source cell, itcan be derived that the UE 410 has the same group member state at thesource cell and the target cell. The group member state indication ofthe UE 410 has already been saved in the source BS 420. Accordingly, itis sufficient to have the saved group member state indication of the UE410 included in the handover request. According to an exemplaryembodiment of the present invention, the group member state indicationcan be arranged only in the event that the UE 410 is the group member,i.e., the handover request does not include the group member stateindication in the event that the UE 410 is not the group member. Thatis, if the group member state indication is included by the handoverrequest, it is indicated that the UE 410 is the group member. Otherwise,it is indicated that the UE 410 is not the group member.

In step 407, the target BS 430 transmits a handover request response tothe source BS 420. Here, the handover request response includes anindication of an X2 signaling context allocated to the UE 410 by thetarget BS 430, and/or an RRC message to be transmitted to the UE 410.The RRC message to be transmitted to the UE 410 is transparentlytransmitted to the source BS 420, and the source BS 420 transfers themessage to the UE 410. If required, the handover request response alsoincludes General Data Transfer Platform (GTP) tunnel information fordata transfer.

In step 409, the source BS 420 transmits an RRC reconfiguration requestto the UE 410. Here, the RRC reconfiguration request includes the “RRCmessage to be transmitted to the UE 410” transmitted to the source BS420 by the target BS 430 in step 407. The “RRC message to be transmittedto the UE 410” is transmitted to the source BS 420 by the target BS 430,and then transmitted to the UE 410 by the source BS 420. Morespecifically, the RRC message to be transmitted to the UE 410 caninclude a Cell Radio Network Temporary Identifier (C-RNTI) allocated tothe UE 410 by the target cell, and/or encryption information of thetarget BS 430, and may further include information of an allocatedrandom access channel.

In step 411, the UE 410 performs synchronization with the target cell.In step 413, the UE 410 transmits an RRC reconfiguration completionmessage to the target BS 430 after completing the synchronization.

In step 415, the target BS 430 transmits a path switching requestmessage to the MME 440, to notify the UE 410 that it has already beenswitched to a new cell, i.e., the target cell. Here, an indication of anS1 signaling context allocated to the UE 410 by the target BS 430 andtunnel information for downlink data reception are included in the pathswitching request message.

In step 417, the MME 440 transmits a path switching response message tothe target BS 430. Here, an indication of an S1 signaling contextallocated to the UE 410 by the MME 440 and/or tunnel information foruplink data are included in the path switching response message, and ifnecessary, encryption information can also be included.

In step 419, the target BS 430 transmits a UE 410 context releasemessage to the source BS 420, to instruct the source BS 420 that thecontext of the UE 410 can be released.

The X2 handover process is implemented as described above.

The above description is provided by taking the source BS and the targetBS corresponding to the same CSG as an example. If the source BS and thetarget BS each correspond to distinct CSGs and the source BS does notsave information of whether the UE can access the target cell, the corenetwork needs to participate in the CSG access control.

FIG. 5 is a diagram illustrating a procedure of a UE accessing a sourcecell required to switch to a target cell according to an exemplaryembodiment of the present invention. The exemplary embodiment of thepresent invention is applied to the system structure illustrated in FIG.3. Here, an X2 interface is established in accordance with the methodillustrated in FIG. 2 between the source BS 520 and the target BS 530.More specifically, the source BS 520 and the target BS 530 can be thehome BS, and can also be the ordinary macro BS supporting a CSGfunction.

Referring to FIG. 5, in step 501, the UE 510 transmits a measurementreport to the source BS 520 in which a source cell is located. Here, theUE 510 transmits the measurement report according to the configurationof the source cell. For example, if it is specified in the configurationof the source cell that the UE 510 transmits the measurement reportperiodically, the UE 510 transmits the measurement report in a presettime interval. If it is specified in the configuration of the sourcecell that the measurement report is triggered by an event, i.e.,transmitted when a certain condition is met, the UE 510 transmits themeasurement report when the event is satisfied. Here, a physical layeridentifier corresponding to the target cell is included in themeasurement report, i.e., the source BS 520 knows the target cell towhich the UE 510 is to be switched. The source cell and the target cellboth may be cells supporting the CSG function. Thus, the CSG identifierand a group member state indication of the UE 510 can be furtherincluded in the measurement report. More specifically, if the groupmember state indication is set as Member, it is indicated that the UE510 is a user member that belongs to the Hybrid cell.

In step 503, the source BS 520 determines whether it is permitted tohandover the UE 510 to the target cell. If the handover is permitted,the source BS 520 transmits an access request to the MME 540 in step505. Otherwise, the source BS 520 refuses to handover the UE 510 to thetarget cell and terminates the current procedure. More specifically, thesource BS 520 can make the determination according to an algorithm forradio resource management and the measurement report in step 503. Thatis, the source BS 520 determines whether a signal of the target cellmeets a handover condition defined by the algorithm for radio resourcemanagement. If it is determined that the signal of the target cell meetsthe handover condition, the source BS 520 determines whether to handoverthe user to the target cell. The source cell in the source BS 520 andthe target cell in the target BS 530 both may be cells supporting theCSG function and correspond to the same CSG. Also, when an X2 interfacebetween the source BS 520 and the target BS 530 is established by themethod illustrated in FIG. 2, the source BS 520 can obtain informationof the CSG supported by the cell in the target BS 530, e.g., the accessmode of the CSG. Also, in the event that the access mode is the Closedmode or the Hybrid mode, the information of the CSG can further includethe CSG ID supported by the cell in the target BS 530. Thus, whendetermining that the signal of the target cell meets the handovercondition defined by the algorithm for radio resource management, thesource BS 520 can also perform a CSG detection function, i.e., determinewhether the CSG ID supported by the target cell is consistent with thatreported in the measurement report by the UE 510. If it is determinedthat the CSG ID supported by the target cell is consistent with thatreported in the measurement report by the UE 510, the source BS 520permits the handover of the UE 510 to the target cell. Otherwise, thesource BS 520 refuses to handover the UE 510 to the target cell if thetarget cell is the CSG cell.

In step 505, the source BS 520 determines that the target cell and thesource cell do not support the same CSG, and then transmits an accessrequest to the MME 540 if the target cell is a cell having a CSGcapability. In an exemplary embodiment of the present invention, inaccordance with the method illustrated in FIG. 2, the source BS 520knows that the cell in the target BS 530 supports the CSG whenestablishing the X2 interface with the target BS 530. Thus, the sourceBS 520 can easily determine whether the target cell and the source cellsupport the same CSG according to the CSG information that is known. Ifit is determined that the target cell and the source cell support thesame CSG, the source BS 520 operates in accordance with the procedureillustrated in FIG. 4. Otherwise, the source BS 520 executes anoperation of transmitting the access request to the MME 540. It shouldbe noted that, if the target cell does not support the CSG function, thecore network does not need to perform a CSG access determination andprocessing is directly performed in accordance with the method in therelated art. Here, the access request can include the CSG ID supportedby the target cell, the access mode and an identifier of the UE 510.

In step 507, the MME 540 controls access of the UE 510 according to theCSG ID supported by the target cell, the access mode and subscriptioninformation of the UE 510, and thereafter, transmits an access responseto the source BS 520. Here, if the target cell is the CSG cell, theaccess response includes an indication of whether the UE 510 ispermitted to have access. Alternatively, in the event that the UE 510 ispermitted to have access, a success access response which indicates thataccess to the target cell is permitted is transmitted. In the event thatthe UE 510 is not permitted to have access, a failure access response,which indicates that access to the target cell is not permitted, istransmitted. If the target cell is the Hybrid cell, the MME 540determines whether the UE 510 is a group user member of the CSGsupported by the target cell. In this case, the access response messagecan include a state indication of whether the UE 510 is the group memberof the Hybrid cell.

In step 509, the source BS 520 determines whether switching the UE 510to the target cell is permitted according to the indication of whetherthe UE 510 is permitted to have access which is included in the accessresponse message. If it is determined that access is permitted, thesource BS 520 transmits the handover request to the target BS 530.Otherwise, the source BS 520 refuses the user to have access andterminates the procedure. Here, at least one of an indication of an X2signaling context allocated to the UE 510 by the source BS 520, anindication by the core network, an indication of an S1 signaling contextallocated to the UE 510 by the core network, an identifier of the targetcell, encryption information and an encryption capability of the UE 510,information of an RRC context and information of an E-RAB are includedin the handover request.

If an access mode of the target cell is the Closed mode, the source BS520 may refuse to switch the user to the target cell in the event thatthe MME 540 instructs that the UE 510 is not permitted to access thetarget cell, and the source BS 520 transmits the handover request to thetarget BS 530 in the event that the MME 540 instructs that the UE 510 ispermitted to access the target cell. In this case, the handover requestcan further include an indication that the UE 510 is permitted to haveaccess, i.e., the UE 510 is permitted to access the CSG supported by thetarget cell. This indication can be explicitly set as an informationelement that access is permitted, or be implicit, which denotes that theMME 540 permits the UE 510 to have access if the source BS 520 hastransmitted the handover request.

If the access mode of the target cell is the Hybrid cell, any of theusers is permitted to access the target cell. Thus, the source BS 520transmits the handover request to the target BS 530. In this case, thehandover request can further include the group member state indicationof the UE 510 at the target cell. More specifically, the group memberstate indication of the UE 510 can be set as “a group member”, i.e., theUE 510 is the user member of the CSG supported by the target cell.Alternatively, the group member state indication of the UE 510 can beset as “not a group member”, i.e., the UE 510 is not the user member ofthe CSG supported by the target cell.

In step 511, the target BS 530 transmits a handover request response tothe source BS 520. Here, the handover request response includes anindication of an X2 signaling context allocated to the UE 510 by thetarget BS 530, and/or an RRC message to be transmitted to the UE 510.More specifically, the RRC message to be transmitted to the UE 510 istransparently transmitted to the source BS 520, and the source BS 520transfers this message to the UE 510. If required, the handover requestresponse also includes General Data Transfer Platform (GTP) tunnelinformation for data transfer.

In step 513, the source BS 520 transmits an RRC reconfiguration requestto the UE 510. Here, the RRC reconfiguration request includes the “RRCmessage to be transmitted to the UE 510” transmitted to the source BS520 by the target BS 530 in step 507. The “RRC message to be transmittedto the UE 510” is transmitted to the source BS 520 by the target BS 530,and then transmitted to the UE 510 by the source BS 520. Morespecifically, the RRC message to be transmitted to the UE 510 caninclude a C-RNTI allocated to the UE 510 by the target cell, and/orencryption information of the target BS 530, and may further includeinformation of an allocated random access channel.

In step 515, the UE 510 performs synchronization with the target cell.In step 517, the UE 510 transmits an RRC reconfiguration completionmessage to the target BS 530 after completing the synchronization.

In step 519, the target BS 530 transmits a path switching requestmessage to the MME 540, to notify the UE 510 that it has already beenswitched to a new cell, i.e., the target cell. Here, an indication of anS1 signaling context allocated to the UE 510 by the target BS 530 andtunnel information for downlink data reception are included in the pathswitching request message.

In step 521, the MME 540 transmits a path switching response message tothe target BS 530. Here, an indication of an S1 signaling contextallocated to the UE 510 by the MME 540 and/or tunnel information foruplink data are included in the path switching response message, and ifnecessary, encryption information can also be included.

In step 523 the target BS 530 transmits a UE 510 context release messageto the source BS 520, to instruct the source BS 520 that the context ofthe UE 510 can be released.

The X2 handover process illustrated in FIG. 5 is implemented asdescribed above.

It can be found that in the above procedure illustrated in FIG. 5, thesource BS triggers the MME to perform the CSG access control, i.e., theaccess control by the MME is executed after the source BS has alreadydetermined to permit the UE to access the target cell. However, in thiscase, the target BS does not participate in the handover procedure. Aprocedure in which the target BS triggers the MME to perform the CSGaccess control is described below with reference to FIG. 6.

FIG. 6 is a diagram illustrating a procedure of a UE accessing a sourcecell in a source BS required to switch to a target cell in a target BSaccording to an exemplary embodiment of the present invention. Theexemplary embodiment of the present invention is applied to the systemstructure illustrated in FIG. 3. Here, an X2 interface is established inaccordance with the method illustrated in FIG. 2 between the source BS620 and the target BS 620. The source BS 620 and the target BS 620 canbe a home BS and an ordinary macro BS supporting a CSG function.

Referring to FIG. 6, in step 601, the UE 610 transmits a measurementreport to the source BS 620 in which a source cell is located. Here, theUE 610 transmits the measurement report according to a configuration ofthe source cell. For example, if it is specified in the configuration ofthe source cell that the UE 610 transmits the measurement reportperiodically, the UE 610 transmits the measurement report in a presettime interval. If it is specified in the configuration of the sourcecell that the measurement report is triggered by an event, i.e.,transmitted when a certain condition is met, the UE 610 transmits themeasurement report when the event is satisfied. Here, a physical layeridentifier corresponding to the target cell is included in themeasurement report, i.e., the source BS 620 knows the target cell towhich the UE 610 is to be switched. The source cell and the target cellboth may be cells supporting the CSG function. Thus, the CSG identifierand a group member state indication of the UE 610 can be furtherincluded in the measurement report. More specifically, if the groupmember state indication is set as Member, it is indicated that the UE610 is a user member that belongs to the Hybrid cell.

In step 603, the source BS 620 determines whether it is permitted tohandover the UE 610 to the target cell. If the handover is permitted,the source BS 620 transmits a handover request to the target BS 620 instep 605. Otherwise, the source BS 620 refuses to handover the UE 610 tothe target cell and terminates the procedure. The source BS 620 can makethe determination according to an algorithm for radio resourcemanagement and the measurement report in step 603. More specifically,the source BS 620 determines whether a signal of the target cell meets ahandover condition defined by the algorithm for radio resourcemanagement. If it is determined that the signal of the target cell meetsthe handover condition, the source BS 620 determines whether to handoverthe user to the target cell. The source cell in the source BS 620 andthe target cell in the target BS 630 both may be cells supporting theCSG function and correspond to the same CSG. Also, when the X2 interfacebetween the source BS 620 and the target BS 630 is established by themethod illustrated in FIG. 2, the source BS 620 can obtain informationof the CSG supported by the cell in the target BS 630, e.g., an accessmode of the CSG. Also, in the event that the access mode is the Closedmode or the Hybrid mode, the information of the CSG can further includethe CSG ID supported by the cell in the target BS 630. Thus, whendetermining that the signal of the target cell meets the handovercondition defined by the algorithm for radio resource management, thesource BS 620 can also perform a CSG detection function, i.e., determinewhether the CSG ID supported by the target cell is consistent with thatreported in the measurement report by the UE 610 If it is determinedthat the CSG ID supported by the target cell is consistent with thatreported in the measurement report by the UE 610, the source BS 620permits handover of the UE 610 to the target cell. Otherwise, the sourceBS 620 refuses to handover the UE 610 to the target cell if the targetcell is the CSG cell.

In step 605, the source BS 620 transmits a handover request to thetarget BS 620. Here, an indication of an X2 signaling context allocatedto the UE 610 by the source BS 620, an indication by the core network,an indication of an S1 signaling context allocated to the UE 610 by thecore network, an identifier of the target cell, encryption informationand an encryption capability of the UE 610, information of an RRCcontext and information of an E-RAB are included in the handoverrequest.

It should be noted that if the source BS 620 has not obtain theinformation of the CSG supported by the cell of the target BS 620 whenthe X2 interface between the source BS 620 and the target BS 620 isestablished, the target BS 620 performs the CSG detection function, andsteps of the CSG detection function, which are alternative steps ofsteps 601 to 605, are as follows. The UE 610 transmits the measurementreport including the CSG ID supported by the target cell and the groupmember state indication of the UE 610 to the source BS 620. The sourceBS 620 transmits the handover request to the target BS 620. In additionto the above information, the handover request should also include thegroup member state indication of the UE 610 and the CSG ID which arereported in the measurement report by the UE 610. After the target BS620 receives the handover request, the target BS 620 compares the CSG IDreported by the UE 610 and the CSG ID actually supported by the targetcell. If the CSG IDs are not consistent with each other, it is indicatedthat the CSG ID reported by the UE 610 is forged. Then in the event thatthe access mode of the target cell is the Closed mode, the target BS 620refuses to switch the UE 610 and transmits a handover failure message tothe source BS 620. In the event that the access mode is the Hybrid mode,the target BS 620 permits to switch the UE 610, but regards the UE 610as being not the group member of the CSG for processing. If the CSG IDsare consistent with each other, it is indicated that the CSG ID reportedby the UE 610 is trustable.

In step 607, the target BS 620 receives the handover request. In step609, if the target cell is the CSG cell, the target BS 620 transmits theaccess request to the MME 640. Here, the target BS 620 transmits theaccess request to the MME 640 to make the core network to determinewhether the UE 610 is permitted to access the target cell. The accessrequest includes the CSG ID supported by the target cell and theidentifier of the UE 610. It should be noted that if the access mode ofthe target cell is the Hybrid mode, any of the users is permitted toaccess the target Hybrid cell. In this case, the transmitting, by thetarget BS 620, the access request to the MME 640 in step 609 andtransmitting, by the MME 640, an access response to the target BS 620 instep 611 may be skipped, and an access control by the target BS 620 instep 613 may be directly performed.

In step 611, the MME 640 controls access of the UE 610 according to theCSG ID supported by the target cell and the subscription information ofthe UE 610, and thereafter, transmits the access response to the targetBS 620. If the access mode of the target cell is the Closed mode, theMME 640 determines whether the UE 610 is permitted to access the targetcell, i.e., the CSG supported by the target cell, according to thesubscription information of the UE 610. In this case, the accessresponse message can include an indication of whether the UE 610 ispermitted to have access. Alternatively, in the event that the UE 610 ispermitted to have access, a success access response which indicates thataccess to the target cell is permitted is transmitted, and in the eventthat the UE 610 is not permitted to have access, a failure accessresponse, which indicates that access to the target cell is notpermitted, is transmitted.

In step 613, if the UE 610 is permitted to access the target cell, thetarget BS 620 performs the access control of the resource according toE-RAB QoS information included by the handover request in step 605, andtransmits the handover request response to the source BS 620. Here, theaccess control in step 607 relies on whether the physical resource inthe target BS 620 can meet requirements of the E-RAB QoS, and asufficient resource is allocated to the E-RAB, which is a currentfunction of the target BS 620. More specifically, the above handoverrequest response includes an indication of an X2 signaling contextallocated to the UE 610 by the target BS 620, and/or an RRC message tobe transmitted to the UE 610, and if required, also includes GTP tunnelinformation for data transfer.

In step 615, the source BS 620 transmits an RRC reconfiguration requestto the UE 610. Here, the RRC reconfiguration request includes the “RRCmessage to be transmitted to the UE 610” transmitted to the source BS620 by the target BS 630 in the above step 607. This “RRC message to betransmitted to the UE 610” is transmitted to the source BS 620 by thetarget BS 630, and then transmitted to the UE 610 by the source BS 620.More specifically, the RRC message to be transmitted to the UE 610 caninclude a C-RNTI allocated to the UE 610 by the target cell, and/orencryption information of the target BS 630, and may further includeinformation of an allocated random access channel.

In step 617, the UE 610 performs synchronization with the target cell,and, in step 619, the UE 610 transmits an RRC reconfiguration completionmessage to the target BS 630 after completing the synchronization.

In step 621, the target BS 620 transmits the path switching requestmessage to the MME 640, to notify the UE 610 that it has already beenswitched to a new cell, i.e., the target cell. Here, an indication of anS1 signaling context allocated to the UE 610 by the target BS 620 andtunnel information for downlink data reception are included in the pathswitching request message. The path switching request message mayfurther include the access mode and the CSG ID supported by the targetcell.

In step 623, the MME 640 transmits the path switching response messageto the target BS 620. Here, an indication of an S1 signaling contextallocated to the UE 610 by the MME 640 and/or tunnel information foruplink data are included in the path switching response message, and ifnecessary, encryption information can also be included. The group memberstate indication of the UE 610, i.e., indication of whether the UE 610is the group member of the target cell, is also included in the pathswitching response message. That is, in step 623, the group member stateindication can be set as “being a group member” or “not a group member”,and can also be set as “being a group member” only. If no setting ismade, the UE 610 is considered as being not the group member. Thus, thetarget BS 620 schedules the UE 610 according to the group member stateindication of the UE 610.

It should be noted that the setting of the group state indication instep 623 is executed when the target cell is the Hybrid cell. The mainreason for this is that any of the Hybrid cells permits the UE 610 tohave access, but in the scheduling, the UE 610 can be scheduled based ontwo roles, i.e., as the group member or not as the group member. If thetarget cell is not the Hybrid cell, e.g., is the Closed cell, it ispossible that the path switching response message does not include thegroup member state indication of the UE 610, which can be similar tostep 415 illustrated in FIG. 4.

In step 625, the target BS 620 transmits the UE 610 context releasemessage to the source BS 620, to instruct the source BS 620 that thecontext of the UE 610 can be released.

The X2 handover process illustrated in FIG. 5 is implemented asdescribed above.

It can be found that in the above procedure illustrated in FIG. 5, it isthe source BS that triggers the MME to perform the CSG access control,and in the above procedure illustrated in FIG. 6, it is the target BSthat triggers the MME to perform the CSG access control. In an exemplaryimplementation, the source BS and the target BS may respectively triggerthe MME to perform the access control, i.e., the source BS triggers theMME to perform the access control of the CSG cell and the target BStriggers the MME to perform the access control of the Hybrid cell, whichis describe in more detail below with reference to FIG. 7.

FIG. 7 is a diagram illustrating a procedure of a UE accessing a sourcecell in a source BS required to switch to a target cell in a target BSaccording to an exemplary embodiment of the present invention. Theexemplary embodiment of the present invention is applied to the systemstructure illustrated in FIG. 3. Here, the X2 interface is establishedin accordance with the method illustrated in FIG. 2 between the sourceBS and the target BS 730. More specifically, the source BS 720 and thetarget BS 730 include a home BS and an ordinary macro BS supporting aCSG function.

Referring to FIG. 7, in step 701, the UE 710 transmits a measurementreport to the source BS 720 in which the source cell is located. Here,the UE 710 transmits the measurement report according to theconfiguration of the source cell. For example, if it is specified in aconfiguration of the source cell that the UE 710 transmits themeasurement report periodically, the UE 710 transmits the measurementreport in a preset time interval. If it is specified in theconfiguration of the source cell that the measurement report istriggered by an event, i.e., is transmitted when a certain condition ismet, the UE 710 transmits the measurement report when the event issatisfied. Here, a physical layer identifier corresponding to the targetcell is included in the measurement report, i.e., the source BS 720knows the target cell to which the UE 710 is to be switched. The sourcecell and the target cell both may be cells supporting the CSG function.Thus, the CSG identifier and a group member state indication of the UE710 can be further included in the measurement report. If the groupmember state indication is set as Member, it is indicated that the UE710 is a user member that belongs to the Hybrid cell.

In step 703, the source BS 720 determines whether it is permitted tohandover the UE 710 to the target cell. If the handover is permitted,the source BS 720 determines that the target cell and the source cell donot support the same CSG in step 705. Otherwise, the source BS 720refuses to handover the UE 710 to the target cell and terminates thecurrent procedure. The source BS 720 can make the determinationaccording to an algorithm for radio resource management and themeasurement report in step 703. More specifically, the source BS 720determines whether a signal of the target cell meets a handovercondition defined by the algorithm for radio resource management. If itis determined that the signal of the target cell meets the handovercondition, the source BS 720 determines whether to handover the user tothe target cell. The source cell in the source BS 720 and the targetcell in the target BS 730 are both cells supporting the CSG function andcorrespond to the same CSG. Also, when an X2 interface between thesource BS 720 and the target BS 730 is established by the methodillustrated in FIG. 2, the source BS 720 can obtain information of theCSG supported by the cell in the target BS 730, e.g., an access mode ofthe CSG. Also, in the event that the access mode is the Closed mode orthe Hybrid mode, the information of the CSG can further include the CSGID supported by the cell in the target BS 730. Thus, when determiningthat the signal of the target cell meets the handover condition definedby the algorithm for radio resource management, the source BS 720 canalso perform a CSG detection function, i.e., determine whether the CSGID supported by the target cell is consistent with that reported in themeasurement report by the UE 710 If it is determined that the CSG ID isconsistent, the source BS 720 permits handover of the UE 710 to thetarget cell. Otherwise, the source BS 720 refuses to handover the UE 710to the target cell if the target cell is the CSG cell.

In step 705, the source BS 720 determines that the target cell and thesource cell do not support the same CSG, and the source BS 720 transmitsthe access request to the MME 740 if the target cell is the CSG cell.Here, the CSG ID supported by the target cell and the identifier of theUE 710 can be included in the access request.

It should be noted that if the access mode of the target cell is theHybrid mode, any of the users is permitted to access the target Hybridcell. In this case, the determining, by the source BS 720, as to whetherthe target cell and the source cell do not support the same CSG and thetransmitting the access request to the MME 740 in steps 705 and thecontrolling of access of the UE 710 according to the CSG ID supported bythe target cell and subscription information of the UE 710 in step 707may be skipped, and an operation of transmitting the handover request tothe target BS 730 in step 709 may be directly performed.

In step 707, an MME 740 controls access of the UE 710 according to theCSG ID supported by the target cell and the subscription information ofthe UE 710, and thereafter, transmits the access response message to thesource BS 720. Here, the access response includes the indication ofwhether the UE 710 is permitted to have access. Alternatively, in theevent that the UE 710 is permitted to have access, a success accessresponse which indicates that access to the target cell is permitted istransmitted, and in the event that the UE 710 is not permitted to haveaccess, a failure access response, which indicates that access to thetarget cell is not permitted, is transmitted.

In step 709, the source BS 720 determines whether it is permitted toswitch the UE 710 to the target cell according to the indication ofwhether the UE 710 is permitted to have access which is included inaccess response message If it is determined that the source BS 720 theswitching of the UE 710 to the target cell is permitted, the source BS720 transmits the handover request to the target BS 730. Otherwise, thesource BS 720 refuses the user to have access and terminates the currentprocedure. Here, if the target cell is the Hybrid cell, any of the usersis permitted to access the target cell, i.e., the source BS 720 directlytransmits the handover request to the target BS 730 in step 709. Here,an indication of an X2 signaling context allocated to the UE 710 by thesource BS 720, an indication by the core network, an indication of an S1signaling context allocated to the UE 710 by the core network, anidentifier of the target cell, encryption information and an encryptioncapability of the UE 710, information of an RRC context and informationof an E-RAB are included in the handover request.

In step 711, if the UE 710 is permitted to access the target cell, thetarget BS 720 performs the access control of the resource according tothe E-RAB QoS information included by the handover request in step 709,and transmits the handover request response to the source BS 720. Here,the access control in Step 707 relies on whether a physical resource inthe target BS 720 can meet requirements of the E-RAB QoS, and asufficient resource is allocated to the E-RAB, which is a currentfunction of the target BS 720. More specifically, the handover requestresponse includes an indication of an X2 signaling context allocated tothe UE 710 by the target BS 720, and/or an RRC message to be transmittedto the UE 710, and if required, also includes GTP tunnel information fordata transfer.

In step 713, the source BS 720 transmits an RRC reconfiguration requestto the UE 710. Here, the RRC reconfiguration request includes the “RRCmessage to be transmitted to the UE 710” transmitted to the source BS720 by the target BS 730 in the above step 707. The “RRC message to betransmitted to the UE 710” is transmitted to the source BS 720 by thetarget BS 730, and then transmitted to the UE 710 by the source BS 720.More specifically, the RRC message to be transmitted to the UE 710 caninclude a C-RNTI allocated to the UE 710 by the target cell, and/orencryption information of the target BS 730, and may further includeinformation of an allocated random access channel.

In step 715, the UE 710 performs synchronization with the target cell,and, in step 717, the UE 710 transmits an RRC reconfiguration completionmessage to the target BS 730 after completing the synchronization.

In step 719, the target BS 720 transmits the path switching requestmessage to the MME 740, to notify the UE 710 that it has already beenswitched to a new cell, i.e., the target cell. Here, an indication of anS1 signaling context allocated to the UE 710 by the target BS 720 andtunnel information for downlink data reception are included in the pathswitching request message. The path switching request message canfurther include the access mode and the CSG ID supported by the targetcell.

In step 721, the MME 740 transmits the path switching response messageto the target BS 720. Here, an indication of an S1 signaling contextallocated to the UE 710 by the MME 740 and/or tunnel information foruplink data are included in the path switching response message, and ifnecessary, encryption information can also be included. The group memberstate indication of the UE 710, i.e., whether the UE 710 is the groupmember of the target cell, is also included in the path switchingresponse message. That is, the group member state indication can be setas “being a group member” or “not a group member”, and can also be setas “being a group member” only. If no setting is made, the UE 710 isconsidered as being not the group member. Thus, the target BS 720schedules the UE 710 according to the group member state indication ofthe UE 710.

It should be noted that the transmitting of the path switching responsemessage by the MME 740 to the target BS 720 in step 721 is executed whenthe target cell is the Hybrid cell. The main reason for this is that anyof the Hybrid cells permits the UE 710 to have access, but in thescheduling, the UE 710 can be scheduled based on two roles, i.e., as thegroup member or not as the group member. If the target cell is not theHybrid cell, e.g., is the Closed cell, it is possible that the pathswitching response message does not include the group member stateindication of the UE 710, which can specifically be similar to step 415illustrated in FIG. 4.

In step 723, the target BS 720 transmits the UE 710 context releasemessage to the source BS 720, to instruct the source BS 720 that thecontext of the UE 710 can be released.

FIG. 8 is a block diagram of a BS in a mobile communication systemaccording to an exemplary embodiment of the present invention.

Referring to FIG. 8, the BS includes a Radio Frequency (RF) processor810, a modem 820, a backhaul communication unit 830, a storage unit 840and a controller 850.

The RF processor 810 performs functions, such as signal band conversionand amplification, to transmit and receive signals over a radio channel.That is, the RF processor 810 up-converts a baseband signal output fromthe modem 820 into the RF signal and transmits the RF signal over anantenna, and down-converts the RF signal received over the antenna intothe baseband signal. Although not illustrated, for example, the RFprocessor 810 may include an amplifier, a mixer, an oscillator, aDigital to Analog Convertor (DAC), an Analog to Digital Convertor (ADC)and the like.

The modem 820 converts the baseband signal and a bit string according toa physical layer standard of the system. For example, to transmit data,the modem 820 generates complex symbols by encoding and modulating atransmit bit string, maps the complex symbols to subcarriers, andconstitutes Orthogonal Frequency-Division Multiplexing (OFDM) symbols byapplying Inverse Fast Fourier Transform (IFFT) and inserting a CyclicPrefix (CP). When receiving data, the modem 820 splits the basebandsignal output from the RF processor 810 into OFDM symbols, restores thesignals mapped to the subcarriers using Fast Fourier Transform (FFT),and restores the receive bit string by demodulating and decoding thesignals.

The backhaul communication unit 830 provides an interface for the BS tocommunicate with other entities (i.e., other BSs, an MME and the like).More specifically, the backhaul communication unit 830 converts the bitstring transmitted by the BS into a physical signal, and converts thephysical signal received at the BS into the bit string. The storage unit840 stores program codes and system information required for theoperations of the BS. The storage unit 840 provides stored data to thecontroller 850 upon a request from the controller 850.

The controller 850 controls the functions of the BS. For example, thecontroller 850 generates a transmit packet and a message and providesthe modem 820 with the transmit packet and the message. The controller850 also processes a receive packet and a message from the modem 820.More particularly, according to an exemplary embodiment of the presentinvention, the controller 850 controls a procedure to establish an X2interface with another BS, a procedure for a handover of an UE fromanother BS to the BS and a procedure for a handover of a UE from the BSto another BS. For example, the controller 850 controls a procedure toestablish an X2 as illustrated in FIG. 2. For example, the controller850 controls a procedure for a handover as illustrated in FIG. 4 to FIG.7.

The backhaul communication unit 830 transmits an X2 interface setuprequest to a second BS, and receives an X2 interface response messagefrom the second BS. Herein, the X2 interface setup request comprises anaccess mode of a Closed Subscriber Group (CSG) supported by a cell onthe first BS. The X2 interface response message comprises the accessmode of the CSG supported by the cell on the second BS. The storage unit840 stores the access mode of the CSG supported by the cell on thesecond BS.

For example, the controller 850 determines whether to permit a handoverof an UE based on an access mode of a target BS, and the backhaulcommunication unit 830 transmits a handover request to the target BS andreceives a handover response from the target BS. Herein, the handoverrequest comprises a group member state indication of the UE.

For example, the backhaul communication unit 830 receives a handoverrequest comprising a CSG ID supported by the target cell which isreported from the UE, and the controller 850 determines whether the CSGID included in the handover request is consistent with the CSG IDsupported by the target cell before transmitting access request. If theCSG IDs are consistent, the backhaul communication unit 830 transmitsthe access request to the MME. However, if the CSG IDs are notconsistent, the backhaul communication unit 830 transmits a handoverfailure message to the source BS.

FIG. 9 is a block diagram of a MME in a mobile communication systemaccording to an exemplary embodiment of the present invention.

Referring to FIG. 9, the MME includes a communication unit 910, astorage unit 920, and a controller 930.

The communication unit 910 provides an interface for a gateway tocommunicate with other entities (i.e., a BS and on the like). Thestorage unit 920 stores program codes and system information requiredfor the operations of the gateway.

The controller 930 controls the functions of the gateway. For example,the controller 930 manages a traffic flow of at least one small BSconnected to the gateway. More particularly, according to an exemplaryembodiment of the present invention, a Handover (HO) processer 932included in the controller 930 controls a procedure for handover of a UEperformed between BSs connected to the MME. For example, the controller930 controls a procedure for a handover as illustrated in FIG. 4 to FIG.7.

According to the exemplary embodiments of the present invention, anaccess mode and a CSG ID supported by the cell at an opposite end can beknown when an X2 interface is established between BSs. Thus, a BS can befacilitated in performing control on access of the UE when serving as asource BS.

Further, a target BS is not configured to request an MME to determinewhether the UE can access the target BS after the UE has already beenswitched to the target BS. Thus, problems resulted from releasing theconnection or handover the UE from the target BS to the source BS by anaccess network when access is not available can be avoided, and normaldata reception by a user can be implemented.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for setting up an X2 interface in amobile communication system, the method comprising: transmitting, by afirst Base Station (BS), an X2 setup request message to a second BS,wherein the X2 setup request message includes a Closed Subscriber Group(CSG) Identifier (ID) and neighbor information of the first BS; andreceiving, by the first BS, an X2 setup response message from the secondBS, wherein the X2 setup response message includes a CSG ID and neighborcell information of the second BS.
 2. A method for a handover in amobile communication system, the method comprising: transmitting, by asource Base Station (BS), a handover request message to a target BS,wherein the handover request message includes a group membership stateof a User Equipment (UE); and receiving, by the source BS, a handoverresponse message from the target BS.
 3. The method of claim 2, furthercomprising: receiving, by the source BS, a measurement reporttransmitted by the UE, wherein the measurement report comprises anidentifier of the target BS.
 4. The method of claim 2, furthercomprising: transmitting, by the source BS, an access request message toa Mobile Management Entity (MME) before transmitting the handoverrequest message; and receiving, by the source BS, an access responsemessage from the MME, wherein the access response message includes anindication of whether the UE is permitted to have access, or, the accessresponse message includes an indication that the UE is permitted to haveaccess and the group membership state of whether the UE is associatedwith a Hybrid cell.
 5. The method of claim 4, wherein the handoverrequest message includes the group membership state of the UE if thetarget cell is a Hybrid cell.
 6. The method of claim 4, furthercomprising: transmitting, by the target BS, the access request messageto an MME if the target cell is a Closed Subscriber Group (CSG) cellbefore transmitting the handover response message, wherein the accessrequest message includes a CSG IDentifier (ID) supported by the targetcell and an identifier of the UE; and receiving, by the target BS, theaccess response message from the MME.
 7. The method of claim 6, whereinthe handover request message includes the CSG ID supported by the targetcell which is reported from the UE, and further comprising: determining,by the target BS, whether the CSG ID included in the handover request isconsistent with the CSG ID supported by the target cell beforetransmitting the access request message, transmitting, by the target BS,the access request message to the MME if the CSG IDs are consistent; andtransmitting, by the target BS, a handover failure message to the sourceBS if the CSG IDs are not consistent.
 8. The method of claim 7, whereinthe access response message is transmitted, by the MME, if the targetcell is the CSG cell and includes an indication of whether the UE ispermitted to have access.
 9. The method of claim 7, wherein the accessresponse message from the MME comprises one of: a success responsemessage if the UE is permitted to have access if the target cell is theCSG cell, and, a failure access response message if the UE is notpermitted to have access if the target cell is the CSG cell.
 10. Themethod of claim 2, further comprising: transmitting, by the source BS,an access request message to a Mobile Management Entity (MME) beforetransmitting the handover request message, if the target cell is aClosed Subscriber Group (CSG) cell; and receiving, by the source BS, anaccess response message from the MME, wherein the access responsemessage comprises an indication of whether the UE is permitted to haveaccess.
 11. The method of claim 2, further comprising: transmitting, bythe source BS, a Radio Resource Control (RRC) reconfiguration requestmessage to the UE; transmitting, by the UE, an RRC reconfigurationcompletion message to the target BS; transmitting, by the target BS, apath switching request message to a Mobile Management Entity (MME),wherein the path switching request message comprises an access mode anda CSG IDentifier (ID) supported by the target cell; transmitting, by theMME, a path switching response message to the target BS, wherein thepath switching response message comprises a group membership state ofthe UE; and transmitting, by the target BS, a UE context release messageto the source BS.
 12. An apparatus for a first Base Station (BS) in amobile communication system, the apparatus comprising: a communicationunit for transmitting an X2 setup request message to a second BS,wherein the X2 setup request message includes a Closed Subscriber Group(CSG) Identifier (ID) and neighbor information of the first BS, and forreceiving an X2 setup response message from the second BS, wherein theX2 setup response message comprises the CSG ID and neighbor informationof the second BS.
 13. An apparatus for a source Base Station (BS) in amobile communication system, the apparatus comprising: a communicationunit for transmitting a handover request message which is transmittedfrom the source BS to a target BS, wherein the handover request messageincludes a group membership state of a User Equipment (UE), and forreceiving a handover response message which is transmitted from thetarget BS to the source BS.
 14. The apparatus of claim 13, furthercomprising: a modem for receiving a measurement report transmitted bythe UE, wherein the measurement report comprises an identifier of thetarget BS.
 15. The apparatus of claim 13, wherein the communication unittransmits an access request message to a Mobile Management Entity (MME)before transmitting the handover request message, and receives an accessresponse message from the MME, wherein the access response messageincludes an indication of whether the UE is permitted to have access,or, the access response message includes an indication that the UE ispermitted to have access and the group membership state of whether theUE is associated with a Hybrid cell.
 16. The apparatus of claim 15,wherein the handover request message includes the group membership stateof the UE if the target cell is a Hybrid cell.
 17. The apparatus ofclaim 15, wherein the access response message includes an indication ofwhether the UE is permitted to have access if the target cell is aClosed Subscriber Group (CSG) cell.
 18. The apparatus of claim 15,wherein the access response message comprises, access if the target cellis a Closed Subscriber Group (CSG) cell, a success response message ifthe UE is permitted to have access and a failure access response messageif the UE is not permitted to have access.
 19. The apparatus of claim13, wherein the communication unit transmits, before transmitting thehandover request message, an access request message to a MobileManagement Entity (MME) if the target cell is a Closed Subscriber Group(CSG) cell, and receives an access response message from the MME,wherein the access response includes an indication of whether the UE ispermitted to have access.
 20. An apparatus for a target Base Station(BS) in a mobile communication system, the apparatus comprising: acommunication unit for receiving a handover request message which istransmitted from a source BS to the target BS, wherein the handoverrequest message includes a group membership state of a User Equipment(UE), and for transmitting a handover response message which istransmitted from the target BS to the source BS.
 21. A method forsetting up an X2 interface in a mobile communication system, the methodcomprising: receiving, by a first Base Station (BS), an X2 setup requestmessage from a second BS, wherein the X2 setup request message comprisesa Closed Subscriber Group (CSG) Identifier (ID) and neighbor informationof the second BS; and transmitting, by the first BS, an X2 setupresponse message to the second BS, wherein the X2 setup response messagecomprises the CSG ID and neighbor cell information of the first BS. 22.A method for a handover in a mobile communication system, the methodcomprising: receiving, by a target Base Station (BS), a handover requestmessage from a source BS, wherein the handover request message includesa group membership state of a User Equipment (UE); and transmitting, bythe target BS, a handover response message to the source BS.
 23. Anapparatus for a first Base Station (BS) in a mobile communicationsystem, the apparatus comprising: a communication unit for receiving anX2 setup request message from a second BS, wherein the X2 setup requestmessage comprises a Closed Subscriber Group (CSG) Identifier (ID) andneighbor cell information of the second BS, and for transmitting an X2setup response message to the second BS, wherein the X2 setup responsemessage comprises the CSG ID and neighbor cell information of the firstBS.
 24. The apparatus of claim 20, further comprising: a controller fordetermining whether a Closed Subscriber Group (CSG) Identifier (ID) of acell in the BS is consistent with the CSG ID of a cell in the source BS,and wherein the communication unit transmits a handover failure messageto the source BS if the CSG IDs are different.
 25. The apparatus ofclaim 13, wherein the group membership state of the UE indicates whetherthe UE is a member of the target BS.
 26. The apparatus of claim 20,wherein the group membership state of the UE indicates whether the UE isa member of the target BS.
 27. The method of claim 22, wherein the groupmembership state of the UE indicates whether the UE is a member of thetarget BS.